620 THE GEOLOGY OP MINNESOTA. 



[Noryte. 



Mic. The section is a poor one. The rock is granular in texture and many of 

 the grains of the ferromagnesian minerals have rounded outlines. The minerals 

 appear to be feldspar, quartz, pyroxene, hornblende and magnetite. The magnetite of 

 this rock was tested for titanium, but none was found. 



One section. 



Age. Probably Keewatin metamorphosed by Cabotian gabbro. 



Eemark. This rock is in general similar to No. 983. u. s. o. 



No. 983. NORYTE(?) ( Granulitic. ) 



Same place as No. 982. 



Ref. Annual Report, xv, pages 351, 352, 392; Annual Report, xxi, pages 144-146. 



Meg. A grayish rock of rather fine grain. The hand specimen is homogeneous 

 throughout and shows no gneissic or other parallel structures. It is compact and 

 not crumbling. Numerous glistening scales of biotite are easily seen, and under the 

 lens the rock appears granular, but the constituent minerals cannot be made out, 

 although one would judge that quartz formed a large part of the rock. Rock appears 

 fresh. Does not effervesce with cold hydrochloric acid. 



Mic. The section shows a closely-compact, fine-grained granular mixture of 

 quartz, feldspar, biotite, iron ore, and a mineral referred to pyroxene. The grain is so 

 fine that under crossed nicols the different grains are not all distinctly separated, nor 

 do some of them extinguish completely; this, however, is due to the overlapping of the 

 grains; there is no " amorphous " or " chalcedonic" silica present (compare section of 

 jaspilyte in Bulletin vi, plate VIII, figure 1). The rock is thus completely crystalline, 

 and is quite fresh. 



The biotite is the most noticeable mineral; it occurs in large flakes which often 

 hold many pieces of quartz, some magnetite, and occasionally pyroxene. 



The pyroxene is in small rounded grains and elongated ones which, however, 

 never show any crystal faces. It has quite a high index of refraction. It contains 

 enclosures of magnetite and numerous transparent areas which seem to be liquid 

 cavities. A slight cleavage is often developed parallel to the long axes of the grains. 

 The extinction is almost always parallel to this cleavage and the mineral often is 

 slightly pleochroic; from these two facts it is referred to the group of orthorhombic 

 pyroxenes probably it is enstatite or bronzite. On account of the smallness of the 

 grain and the difficulty of obtaining a good interference figure with the instrument 

 in use, the optical properties were not further studied. This mineral is greenish in 

 color. In the pleochroic individuals the ray vibrating parallel to the cleavage is 

 colorless or greenish and the other of a very light pinkish or reddish shade. This 

 corresponds to the pleochroism of orthorhombic pyroxenes, Monoclinic pyroxene 

 is probably present in small amount, 



